Photopolymerization apparatus

ABSTRACT

Process and apparatus for polymerizing oxygen-inhibited ultraviolet photopolymerizable resin-forming material such as a film is shown. The apparatus comprises a pair of U.V. light sources, one being a flash photolysis source, the other a sustained photolysis source, both disposed for irradiating said mass as it abides in an atmosphere such as air which tends to inhibit such polymerization. The process has two essential phases, a superficial phase and a profound phase, performed simultaneously or one in advance of and as preparation for the other. The profound phase is performed with sustained irradiation effective for substantially completely polymerizing said material except for inhibition of polymerization at the surface thereof due to said atmosphere. The superficial phase is performed with flash irradiation effective for forming a tack-free skin over said material. Said skin helps to protect the less fully polymerized material therebelow from oxygen inhibition when such superficial phase is performed first or simultaneously with the other phase. When such superficial phase is performed after the profound phase, said superficial phase acts to complete polymerization of said material throughout its thickness.

United States Patent DeSorgo et a].

[ PHOTOPOLYMERIZATION APPARATUS [75] Inventors: Miksa DeSorgo, Olmsted;Vincent D.

McGinniss, Middleburgh Heights, both of Ohio [73] Assignee: SCMCorporation, Cleveland, Ohio [22] Filed: June 25, 1973 [2]] Appl. No.:373,374

Primary E.tuminer-Howard S. Williams Attorney, Agent. or Firm-Thomas M.Schmitz [57] ABSTRACT Process and apparatus for polymerizing oxygen- U.V. FL 45H PHOTOLYE/fi SOURCE llllllll POSITION 1 1 Apr. 1,1975

inhibited ultraviolet photopolymerizable resin-forming material such asa film is shown. The apparatus comprises a pair of U.\/. light sources,one being a flash photolysis source, the other a sustained photolysissource, both disposed for irradiating said mass as it abides in anatmosphere such as air which tends to inhibit such polymerization. Theprocess has two essential phases, a superficial phase and a profoundphase, performed simultaneously or one in advance of and as preparationfor the other. The profound phase is performed with sustainedirradiation effective for substantially completely polymerizing saidmaterial except for inhibition of polymerization at the surface thereofdue to said atmosphere. The superficial phase is performed with flashirradiation effective for forming a tack-free skin over said material.Said skin helps to protect the less fully polymerized materialtherebelow from oxygen inhibition when such superficial phase isperformed first or simultaneously with the other phase. When suchsuperficial phase is performed after the profound phase, saidsuperficial phase acts to complete polymerization of said materialthroughout its thickness 4 Claims, 1 Drawing Figure U- V. $U5TA [NEDDHOTOLYS/S SOUQCE l6 POSITION 2 PATENTEUAPR' 1 ms 1 PHOTOPOLYMERIZATIONAPPARATUS BACKGROUND OF THE INVENTION This invention relates to processand apparatus for polymerizing oxygen-inhibited ultravioletphotopolymerizable resinforming material such as a film or a depositthereof on a substrate. For convenience herein such masses of theresin-forming material will be referred to from time to time simply asfilms.

Superficial curing herein connotes polymerization of the binding vehiclein such film to convert the surface of the film from a liquid or tackycondition into a tackfree condition, detectable by touch; full curingconnotes substantially complete polymerization of the film throughoutits thickness to a finished state. Films that undercured often have pooradhesion to substrates. Films with mainly a superficial cure (andsomewhat undercured therebelow) frequently will develop defects such aswrinkling, orangepeeling," or alligatoring. Films that are well curedbelow, but which have a tacky or undercured surface, are generallyunusable because of such tacky or undercured and thus unsatisfactorycondition.

The generally advantageous ultraviolet wave energy useful for theinstant process is that U.V. energy in the so-called near-visible" ornear-U.V. region, in other words, the wavelengths of the U.V. spectrumthat are transmittable through a quartz or other transparent window.Such advantageous range should be understood herein as lying betweenabout l,600-l,800 A wavelength and about 4,0004,200 A wavelength, andpreferably between about 2,500 A and 4,000 A wave length.

Conventionally convection ovens and infrared sources have been used tocure (polymerize) films in the nature of a paint, varnish, enamel,lacquer, stain, filler, ink, or adhesive. The instant film or depositcan be a clear one, optionally tinted, or an opaque one, either kind ina variety of colors for the purpose of protecting, decorating, and/orapplying a message on a substrate, or for adhesively uniting a pluralityof U.V. light-transmitting layers one with another. For convenienceherein the film or deposit for such curing, whether it is virtuallytotally polymerizable, such as a binding-type vehicle by itself, or suchvehicle compounded with other ingredients such as pigments and fillers,will be referred to herein from time to time as a paint." Such paint"can be a fluent, liquid phase continuous material, a jelly likematerial, or a powdery mixture. It can have, if desired, opacifyingpigment and/or added colorants and fillers in conjunction with suchpolymerizable binding vehicle. Such paint also can have various otherconventional additives such as pesticides, odorants, flow-controlagents, bubble breakers, defoamers, plasticizers, intercoat adhesionpromoters, and other ingredients conventional in surface-coating filmsand adhesives.

More recently ultraviolet wave energy curing of materials has beensuggested, usually using various U.V. sensitizers for sensitizingphotopolymerization in ultraviolet wavelengths in the near-visibleregion. The literature on such photopolymerization and sensitization isabundant. Films (deposits) of paint for such U.V. curing can be quitethin, e.g., 0.1 mil or less, often are 0.5-2 mils in thickness, and canbe as high as 50 or 60 mils, although heretofore such extremely thickfilms have often been difficult to cure. For the purpose of thisspecification, films (including deposits) can be continuous ordiscontinuous upwards to the thickness of mils.

A fairly intense radiation source which emits a minor proportion of itsradiation in the near-U.V. region is shown in US. Pat. Nos. 3,364,387and 3,650,669; the latter patent teaches the curing of paint films byexposure to such radiation. This sustained source of U.V. energy isconveniently described as a plasma arc torch operating at essentiallyatmospheric pressure. It usually operates with a swirl flow. Theintensity of such torch integrated throughout the entire spectrum rangeof its continuum light radiation can be at least about 350 watts persquare centimeter steradian. Ordinarily, such apparatus is used with aninert gas atmosphere blanketing the coated workpiece to be irradiated soas to prevent inhibition of polymerization from air.

Electric lamps and lasers have been made to emit sustained U.V.radiation also for such curing purpose. An example of laser applicationto the cure of U.V.-polymerizable materials is in the copending US.patent application of Antonio de Souza and A. M. Buhoveckey, U.S. Ser.No. 189,254, filed Oct. 14, 1971. Other examples of U.V. laser and U.V.electric lamp curing of such materials are shown in US. Ser. No. 342,038of Antonio de Souza, filed Mar. I6, 1973.

Commercial electric U.V. lamps for this sustained curing purpose areshown, for example, in U.S. Pat. Nos. 3,499,781 and 3,673,140. Suchcommercial lamps are usually referred to as mercury U.V. lamps" eventhough they can have gases mixed with the mercury which modify theemanations. They ordinarily have medium filling pressure. U.V. lightsources for flash photolysis also can be conventional and devised onprinciples related to the sustained electrical U.V. photolysis lightsources except that they are controlled to emit short bursts or flashesof energy interrupted by down time. A typical flash photolysis source isshown in West German Pat. No. 2,019,270 of Nov. 16, I972. The subjectmatter of these patents and all the patent applications cited herein isexpressly incorporated herein by reference.

Molecular oxygen in the atmosphere surrounding the film usually isinhibitory to the full curing of otherwise U.V.-photopolymerizableresin-forming masses. In such instance often the surface in contact withsuch atmosphere remains undercured. Additionally, any ozone present isespecially so inhibiting. Hence the masses to be cured usually areprotected from air atm osphere with nitrogen or other inert blanketinggas at considerable expense and trouble. Such inhibiting atmosphere alsocan be substantially more or less rich in molecular oxygen than air isand still be quite inhibitory to satisfactory curing of the film ordeposit.

Advantages of U.V. curing over other conventional curing in ovens or thelike include especially the ability of the U.V. irradiation to performcold polymerization (curing") of the film at high speed with attendantsuppression of losses due to volatilization of components of the film,suppression of discoloration or degradation of the film, suppression ofshrinkage and distortion of the film and of the substrate (preservationof dimensional stability), and suppression of degradation of thesubstrate to which the film is applied, particularly when such substrateis plastic, paper, or fabric.

Special advantages of the instant invention include effective U.V.curing of the films or deposits in economical atmospheres such as air, alessened cooling load on the individual U.V. light sources of theapparatus, and the ability to distribute such load over a plurality ofU.V. light sources. The sustained operation of U.V. lamps at about theirhighest intensity often overheats them and causes production slowdowns.This invention permits, in many cases, beneficial reduction of energyintensity from the sustained irradiating U.V. light source or sourcesused according to invention principles.

SUMMARY OF THE INVENTION The instant improvement in a process forpolymerizing an oxygen-inhibited ultraviolet photopolymerizableresin-forming material by exposing a surface thereof to U.V. radiationcomprises:

subjecting the exposed surface of said material to superficialpolymerization initiated by a flash of U.V. energy effective for forminga tack-free skin over said mass during, prior to, or subsequent tophotopolymerizing the balance of the material below said exposed surfaceby sustained U.V. irradiation.

Imaging reflectors can be used to direct both the superficial and thesustained U.V. irradiation onto the same surface area for simultaneousperformance of both phases. Alternatively, and preferably for greaterflexibility in the process, the sustained phase and the superficialphase can be conducted as follows:

staging said polymerization process as two essential phases,specifically a superficial phase and a profound phase, and

performing one of said phases in advance of and as preparation for theother with both in the ambience of atmosphere containingpolymerizationinhibiting oxygen,

said profound phase being performed with sustained irradiation by saidU.V. energy effective for substantially completely polymerizing saidmass except for inhibition of polymerization at the surface thereof dueto said oxygen,

said superficial phase being performed with a flash of said U.V. energyeffective for forming a tack-free skin over said mass and, in so doing,either a. improving protection of the less fully polymerizedresin-forming material therebelow from polymerization inhibition due tosaid oxygen when said superficial phase is the first one to beperformed, or

b. substantially completing polymerization of said mass throughout itsthickness when said superficial phase is the second one to be performed.

The instant apparatus for polymerizing such resinforniing material by soirradiating it comprises a pair of light sources providing said U.V.energy, one of said pair being a flash photolysis light source, theother of said pair being a sustained photolysis light source, both ofsaid sources being disposed for irradiating said mass simultaneously orsequentially as it abides in an atmosphere containingpolymerization-inhibiting oxygen.

The kind of polymerizable vehicle in the film will affect the intensityuseful for curing the film rapidly, as well as will the thickness ofsuch film, kind and proportion of pigmentation and/or dye in the film,the gaseous atmosphere around the film, the type of sensitizers or otherpolymerization activators and their proportion in the film, and thewavelength or wavelengths emanated from the particular ultravioletsource of radiation being used in the near-visible region. That is tosay, thicker films up to thicknesses of 35 mils but even more generallyl.52.5 mils often will call for a higher critical intensity than thinnerfllms of the same material, as will kinds and proportions of pigments,dyes and mineral fillers, the particular wavelengths of light availablefrom the source in the near-U.V. region, and all those things which tendto absorb or transmit the particular U,V. energy being utilized, as wellas the activity of the particular sensitizer system and the inertness ofthe gas atmosphere towards the film surface. As a practical matter aU.V. sensitizer or sensitizer mixture is used in virtually every filmfor this photopolymerization.

DESCRIPTION OF THE DRAWING The drawing is a flow diagram of one simpleform of the invention using conventional light sources providing theU.V. energy sequentially as preferred. Con veyor deck 13, traveling fromleft to right, positions substrate ll (suitably wood or metal) atposition i. Substrate i1 is coated on its top surface with a film ofoxygen-inhibited ultraviolet photopolymerizable resinforming material12. The ambient atmosphere surrounding this coating at this position andalso at position 2 is air. Conventional flash photolysis light source 15then is turned on to flash irradiate the top surface of film 12 withU.V. energy depicted as rays 14, this irradiation being effective forforming a tack-free skin superficially over the top of coating 12.Conveyor deck 13 then moves coated workpiece 11 to the right and toposition 2 beneath conventional sustained photolysis light source 16.The pre-treated workpiece in position 2 is indicated as item 11', andthe thus-pretreated coat ing thereon as 12'. The rays emanating from thesustained U.V. photolysis source are depicted as item 17. This exposureto sustained irradiation can last from a few milliseconds up to severalseconds and is called for convenience herein the profound phase." Itsubstantially completely polymerizes the remainder of the coatingthroughout its thickness; the underlying resinforming material in thisinstance is protected from polymerization inhibition by virtue of theskin formed over the coating in the earlier or superficial phase of theoperation.

When the conveyor deck travel is reversed in direc tion with the freshlycoated workpiece traveling from right to left, then the followingoccurs: the profound phase substantially completely polymerizes the massof the film except for inhibition of polymerization at the surfacethereof due to the air environment. The thustreated workpiece is thenmoved leftwardly and positioned under the flash U.V. photolysis source,and the polymerization of the entire film mass is substantiallycompleted throughout its thickness. In either case the high intensity ofthe U.V. flash can be used to overwhelm the inhibition to cure.

Obviously multiple flash photolysis light sources can be used ifnecessary or desirable. Frequently it. can be desirable to have two ormore of such sources operating in sequence as workpieces travel beneaththem on a conveyor. When such flash units are off, they can be coolingeffectively and advantageously. Similarly, a plurality of sustained U.V.photolysis sources can be used in a series to provide adequate energydosage for effecting the profound phase of the film curing. The lightsources can use imaging means such as reflectors to direct andconcentrate their beams on the films being treated.

Usually the freshly coated workpieces are moved continuously by conveyorunder the flash and sustained U.V. units. However, it is conceivable tomove or refocus these light sources relative to the workpiece positionor to use one conveyor for one phase of the operation and another forthe second phase.

Flash photolysis operates extremely rapidly, the irradiation oftenlasting only 1/1 ,000 to l/l00,000 of a second, typically about [[50,000of a second. The U.V. energy can be quite intense, e.g., up to severalwatts per square cm. or, advantageously, much higher, e.g., hundreds orthousands, if desired, or it can be of an intensity as low as a few tensof milliwatts per square cm. of the exposed film. Flash photolysis unitsemitting a fairly continuous spectrum of near-U.V. light energy areavailable, for example, a xenon gas-containing lamp, from the XenonCorporation. Usually they are operated off a condenser bank in which isbuilt up a highvoltage electrical charge to light the lamp periodically.Alternatively, a pulsed near-U.V. laser of high output energy, e.g., anitrogen laser, also can be used. The pulses can be, for example, from 1to 500 per second and last about a monosecond. Optical means can be usedto spread, concentrate, and scan light beams over the work. Sustainedphotolysis units are designed to irradiate substantially continuouslyeven though they might be using alternating electric current which makesfor variable output.

Typically the polymerizable film-forming material can constitute theentire film or be the polymerizable binder for discrete, substantiallyinert solids and additives therein such as pigments to yield the curedproduct in the nature of a paint, varnish,enamel, lacquer, filler,stain, ink, or adhesive. Preferably the uncured films are fluent atordinary irradiation temperature (between about 30F. and about 300F. andadvantageously between ordinary room temperature and about 180F.). Whenpolymerized in accordance with this invention, a tackfree film that isdurable enough for ordinary handling results rapidly. In the cured statethe binder of such film is resinous or polymeric in nature, oftencrosslinked. Uncured for application to a substrate or uncured on suchsubstrate, such paint consists essentially of a monomer or a mixture ofmonomers, or a further polymerizable oligomer, prepolymer, resin, ormixture of same, or a resinous material dispersed or dissolved in asolvent that is copolymerizable therewith. Such solvent ordinarily ismonomeric, but can be an oligomer (i.e., up to 4 monomer unitsconnected) or prepolymer (molecular weight rarely above about 2,000).Oligomers and prepolymers should be understood herein as being polymericin nature.

ln the main such vehicles or binders are those which also areconventionally polymerizable by free-radicalinduced additionpolymerization using peroxy or azo catalysis or a redox system.Alternatively, however, the binders can be a fluent material wherein theultraviolet wave energy causes photochemical generation of a catalyticmaterial or effects a rearrangement which starts a polymerization thatcontinues until a usefully polymerized deposit results. The usefulvehicles can be polymeric, monomeric, or a mixture, especially thoseexhibiting polymerizable vinyl, acrylic, allylic, mercaptan, fumaric,maleic, or like unsaturated functionality. Reactive polymeric typesinclude unsaturated polyesters, acrylics, epoxies, urethanes, andsilicones. Representative polymeric vehicles include those derived fromthe reaction of dibasic acids or their anhydrides with polyols. Forexample, equimolar amounts of maleic anhydride and phthalic anhydridecan be condensed with propylene glycol in slight excess to form anunsaturated polyester which can be diluted with styrene to a sirup ofresin solids, generally between 40 and 80 percent n.v. The polyesterresin thus prepared has an acid number of about and less. Furnaric acidcan be substituted for the maleic anhydride. Similarly, propylene oxidecan be substituted for the major portion of propylene glycol. Alsoinstead of styrene other copolymerizable monomers such ashydroxyethylacrylate can be used.

Other useful types for curing include trimethylolpropane triacrylate,pentaerythritol triacrylate, ethyleneglycol diacrylate, diacrylic acidadduct of the diglycidyl ether of bisphenol A (DER 332 diacrylate), adior tri-isocyanate reacted with a hydroxy-containing acrylate such ashydroxyethyl or hydroxypropyl acrylate.

Reactive monomer types include a variety of acrylates such ashydroxyethyl, cyclohexyl, hydroxypropyl, Z-ethylhexyl, benzyl,phenoxyethoxy, lower alkoxyethoxy, tetrahydrofurfuryl, and similaracrylates, and also N-vinyl pyrrolidone, vinyl acetate, vinylacetatebutyrate, styrene and substituted styrenes. The most popularcurable film binders for treatment in accordance with the instantinvention contain at least one polymerizable ethylenically unsaturatedgroup of the structure:

Sensitizer types useful in promoting U.V. polymerization of the film inaccordance with the instant invention include the types:chlorosulfonated polynuclear ketones blended with alphahaloalkylatedpolynuclear ketones; chlorosulfonated benzanthrones blended withalpha-haloalkylated benzanthrones; chlorosulfonated fluorenones plusalpha-haloalkylated fluorenones; carbonylated phenyl nuclear sulfonylchlorides; and carbonylated polynuclear sulfonyl chlorides as shown inthe copending US. Pat. applications of Vincent R. McGinniss, Ser. Nos.323031, 323087, 323032, and 323086, respectively, expressly incorporatedherein by reference. Other sensitizers that are conventional can be usedalone or in admixture with the foregoing ones, for example, benzoin,benzoin ethers, oxime ethers, and phosphines. While the speed of U.V.curing is quite remarkable using the present invention technique, thedepth of cure also is usually quite practical so that the resultingpolymerized deposit not only is tack-free, but also resists scratchingor disruption when first ostensibly tack-free. Curing can continue onstored pieces. Typically substrate work-pieces coated with the uncuredpaint deposit or deposits are passed transversely to the U.V.-providinglight beam by a conveyor. The substrate being coated can be metal,mineral, glass, wood, paper, plastic, fabric, ceramic, etc.

Many useful pigments can be incorporated, in modest proportions, intothe vehicle without much deleterious effect. Thus, opacifying pigmentssuch as zinc oxide can be used quite well. Titania, e.g., anatase andparticularly rutile, makes for a much more difficult film to cure byU.V. radiation, but such opacifying pigmentation can be used. Otherfiller materials and coloring pigments such as basic lead sulfate,magnesium silicate, silica, clays, wollastonite, talcs, mica, chromates,iron pigments, wood flour, microballoons, hard polymer particles, andeven reinforcing glass fiber or flake also are suitable in the vehicleto make a paint. Ordinarily it is most desirable to use pigments whichdo not absorb a great deal of U.V. wavelength in the same region of theU.V. spectrum as is absorbed by the U.V. sensitizer. However, by use ofadjunct energy-transferring, U.V.- sensitizing materials such asMichlers ketone in the sensitizing mixture, sufficient energy transferoften can be obtained to activate sensitizers such as the carbonylatedphenyl nuclear sulfonyl chloride types and enhance the curing ofpigmented systems. The wavelength of the U.V. source should not be toosimilar to or close to the wavelength absorbed by the pigment in theU.V. range for best advantage of the irradiation process. Pigmented orfilled films for the process preferably are no more than about a milthick and generally about (Ll-0.5 mil thick maximum, for efficiency andeconomy of curing.

In this specification, unless otherwise expressly indicated, all partsare parts by weight, all percentages are weight percentages, and alltemperatures are in degrees Fahrenheit.

The superficial phase of this curing operation merely polymerizes theresin-forming material into a protective skin which is either sufficientto substantially complete polymerization of the mass when it has beentreated in the profound phase previously or to protect the lessfullypolymerized resin-forming material therebelow from polymerizationinhibition when said superficial phase is the first one to be performed.The superficial phase and the profound phase are, of course, susceptibleto being divided up into a series of subsuperficial and "subprofound"phases, each of said series acting simultaneously or sequentially toperform a complete superficial phase or a complete profound phasecollectively. The profound or in-depth curing phase will substantiallycomplete polymerization throughout the mass, except for the top surfacethereof exposed to oxygen inhibition or previously skinnedover by thesuperficial phase of the irradiation. The superficial phase will formthe skin" at the top surface and effect minor polymerization into thedepth of the film, perhaps affecting only l-40 percent of the film depthby way of polymerization to some appreciable degree.

The following example shows how my invention can be practiced, butshould not be construed as limiting the invention.

EXAMPLE Component Parts by Weight The reaction product of 1 mol ofisophorone diisocyanate and 2 mols of hydroxyethylacrylate 40Hydroxyethylacrylate 25 2-phenoxyethylacrylate -Continued ComponentParts by Weight Melamine acrylate l5 Sensitizing mixture: Benzo henoneThe freshly coated side of the panel is subjected to irradiation from aXenon Corporation flash photolysis lamp operating to emit asubstantially continuous spectrum of U.V. energy in the 2,000-4,000 Arange of wavelength. The gap of atmospheric air at room temperaturebetween the lamp and the panel is about 4 inches. The lamp emits suchenergy for up to about 111,000 second.

The lamp is about 8 inches long and 10 mm. in diameter and housed in anelongated housing of essentially square cross section that is blackinside. The U.V. light is emitted from a l-inch diameter exit port about1 inch in front of the lamp surface and mid-way to the length of thelamp tube. The power supply is 400 volts d.c. charging a bank of 10capacitators parallel, each of I00 microfarads rating. The housing actspoorly as a reflector; it is estimated that about k to l Joule ofnear-U.V. energy per flash is the near-U.V. light output through suchexit port.

A superficial top surface cure results on the paint of the panel struckby the flash of U.V. energy. This area of the paint is non-tacky to thetouch, but examination shows that the film is soft and decidedlyunderpolymerized slightly below its surface and further to its bottom.The thus-treated panel then is passed, paint-side-up, by conveyorsuccessively under a pair of like commercial mercury vapor lamps inparallel array and designed for emitting near-U.V. energy. These lampsare l-lanovia model No. 652-OA43l U.V. lamps having a 4,000-watt demand,and they are 20 inches long. Each is equipped with an efficientreflector. The conveyor travel is normal to the axis of said lamps and 6inches below said lamps at the rate of about feet per minute. Air is theatmosphere between lamps and panel. The result is a fully cured(substantially completely polymerized throughout) paint film havingexcellent adhesion, gloss, and resistance for its type.

We claim:

1. In combination with an ultraviolet photopolymerizable material, anapparatus for irradiating a mass of said material located within anirradiation area and disposed within an air-inhibited atmospherecomprising:

a first ultraviolet light source for irradiating said material withinsaid irradiation area, said first source being a flash photolysis lightsource emitting pulse irradiation whereby said material is curedsuperficially;

a second ultraviolet light source for irradiating said material withinsaid irradiation area, said second source being a sustained photolysislight source emitting substantially continuous ultraviolet light wherebysaid material is profoundly cured.

2. The apparatus in claim 1 wherein said first source emits betweenabout 1 to 500 pulses per second, each said pulse irradiating betweenabout 1]] ,000 to l/ 100,000 of a second.

3. The apparatus of claim 1 wherein said first source irradiatessimultaneously with said second source.

4. The apparatus of claim 1 wherein said first source irradiatessequentially with said second source.

in a: a: a:

1. IN COMBINATION WITH AN ULTRAVIOLET PHOTOPOLYMERIZABLE MATERIAL, ANAPPARATUS FOR IRRADIATING A MASS OF SAID MATERIAL LOCATED WITHIN ANIRRADIATION AREA AND DISPOSED WITHIN AN AIR-INHIBITED ATMOSPHERECOMPRISING: A FIRST ULTRAVIOLET LIGHT SOURCE FOR IRRADIATING SAIDMATERIAL WITHIN SAID IRRADIATION AREA, SAID FIRST SOURCE BEING A FLASHPHOTOLYSIS LIGHT SOURCE EMITTING PULSE IRRADIATION WHEREBY SAID MATERIALIS CURED SUPERFICIALLY; A SECOND ULTRAVIOLET LIGHT SOURCE FORIRRADIATING SAID MATERIAL WITHIN SAID IRRADIATION AREA, SAID SECONDSOURCE BEING A SUBSTAINED PHOTOLYSIS LIGHT SOURCE EMITTING SUBSTANTIALLYCONTINUOUS ULTRAVIOLET LIGHT WHEREBY SAID MATERIAL IS PROFOUNDLY CURED.2. The apparatus in claim 1 wherein said first source emits betweenabout 1 to 500 pulses per second, each said pulse irradiating betweenabout 1/1,000 to 1/100,000 of a second.
 3. The apparatus of claim 1wherein said first source irradiates simultaneously with said secondsource.
 4. The apparatus of claim 1 wherein said first source irradiatessequentially with said second source.